Solvent extraction process using dimethyl hydrogen phosphite



Jan. 16, 1962 w. B. WATSON- 3,017,346

SOLVENT EXTRACTION PROCESS usmc DIMETHYL HYDROGEN PHOSPHITE Filed Oct. 15, 1959 D'METHVL HYDROGEN k PHOSPH/TE D/LUENT a! 57 v E R 1L & FLASH E RAFF/NATE gT/LL 0 STREAM RAFF/NATE A4 k R \f SETTLER 2 o 2 R -J u 5; SLUDGE 35 Ct 12 & N l0 FLASH E EXTRACT STILL STREAM N -=,xrRAcT HYDROCARBON FEED INVENTOR WILL/AM B. WATSON BYM Z4 ATTORNEY United States Patent Ofiice 3,017,346 Patented Jan. 16, 1962 Maine Filed Oct. 15, 1959, Ser. No. 846,599 4 Claims. (Cl. 208-322) This invention relates to the separation of mixtures of hydrocarbons by means of selective solvents. More specifically this invention relates to the separation of hydrocarbon mixtures into a relatively aliphatic fraction and a relatively aromatic fraction.

It is well known in the art to treat mineral oils, particularly petroleum oils, with selective solvents in order to segregate the relatively more aliphatic fractions from the relatively more aromatic fractions. In these processes, various solvents are used, as for example, solvents of the class which have a preferential selectivity for the more aromatic type compounds, as compared to the more aliphatic type compounds. Solvents of this class are, for instance, phenol, furfural, liquid sulfur dioxide, nitrobenzene, cresol and aniline.

With the commercial development of new processes for producing aromatic hydrocarbons on the one hand and for improving hydrocarbon products such as distillate fuels and lubricating oils by the removal of aromatic components on the other, there has been an increased demand for processes involving separation of aromatic fractions from hydrocarbon mixtures containing the same.

It has now been found that dimethyl hyrogen phosphite is effective for the selective extraction of aromatic hydrocarbons from other hydrocarbons, particularly saturated hydrocarbons. It has further been discovered that dimethyl hydrogen phosphite in addition to exhibiting selective solvency characteristics toward the aromatic hydrocarbons, is reactive with olefinic hydrocarbons to form a sludge. Consequently, dimethyl hydrogen phosphite possesses the advantage of removing unstable components by yielding a sludge while segregating an aromatic extract fraction. The type of reaction between dimethyl hydrogen phosphite and the hydrocarbon that can occur to produce a sludge can be illustrated as follows:

The liquid hydrocarbon feeds of this invention contain substantial quantities of both aliphatic and aromatic hydrocarbons and include, for instance, lubricating oils, fuel oils and gas oils as well as mixtures of other natural or synthetic hydrocarbons, and feeds with a low concentration of olefins are preferred.

Dimethyl hydrogen phosphite is a water white liquid with a boiling point of 160 F. (25 mm. Hg) and a specific gravity of 1.200 (25 C./25 C.). It may be employed alone in the present invention or in conjunction with diluents such as, for instance, benzene aromatics such as benzene, toluene and xylene.

In accordance with the present invention a liquid hydrocarbon mixture containing aromatic and aliphatic, including cycloaliphatic, hydrocarbons is contacted with a a suitable proportion of the dimethyl hydrogen phosphite. A liquid extract phase containing the more aromatic fraction of the feedstock is produced. The more aliphatic raflinate phase is then separated from the extract phase, and the dimethyl hydrogen phosphite and other solvent,

if employed, is removed from the separated layers by any suitable means known in the art, e.g. distillation of the phosphite and other solvent. Likewise, the sludge formed can also be removed from the separated layers by any suitable means, as for instance, by settling.

In conducting the extraction the amount of solvent employed is that suflicient to form two liquid phases. The

proportion usually falls within the range of about 0.5 to 30 volumes of solvent per volume of hydrocarbon feed and preferably about 0.5 to 10 volumes of solvent per volume of feed. If the solvent is composed of a blend of dimethyl hydrogen phosphite and a diluent, the diluent will generally comprise up to about 50% of the blend. In the practice of this invention either continuous, semicontinuous or batch processes may be employed. Known types of solvent extraction equipment and operations can be used.

The temperature and pressures maintained on the solvent extracting system can vary widely depending upon the hydrocarbon mixture being treated, the solvent to oil ratio as well as upon whether dimethyl hydrogen phosphite is being used alone or in conjunction with other extractive solvents. In general, the temperatures used range from about to 300 F. The pressure employed is that suflicient to maintain the constituents in the liquid phase.

To further illustrate the present invention a representative operating procedure is described in conjunction with the attached drawing.

The hydrocarbon feed to be extracted is charged through line 1 to extraction tower 2. The extraction solvent, i.e. dimethyl hydrogen phosphite alone or blended with other diluents, is introduced through line 3 and 3 into recycle line 7 and hence to extractor 2. In the extraction zone the hydrocarbon feed is countercurrently contacted with the solvent. The rafiinate stream passes overhead and is sent via line 4 to flash still 5 and hence to stripper 6 for the removal of the solvent. Steam or an inert gas, such as nitrogen can be used for stripping. However, since water reacts with dimethyl hydrogen phosphite, an inert gas is generally preferable. The solvent removed is recycled through line 7 to the extraction tower. The bottoms product from the raflinate stripper 6 is sent via line 8 to settler 9 where the sludge is separated from the raifinate. If desired, water can be injected in the raffinate stream prior to the settler in order to facilitate sludge removal.

Returning now to extractor 2, the extract stream is recovered from the bottom of the extraction tower and sent through line 10 to flash still 11 and hence to stripper 12. The solvent removed is recycled via line 7 to extraction tower 2. If desired, the bottoms product from stripper 12., i.e. the extract, is sent to a settler (not shown) to separate sludge. Make-up solvent can be introduced via lines 3 and 3. When blends of dimethyl hydrogen phosphite and diluents are employed, the recycled solvent can be sent to a fractionator to recover the phosphite and diluents for reblending prior to recycle. This step permits using different solvent compositions for treating different hydrocarbon blends in one unit or for treating one blend at a variety of conditions.

Four examples illustrating the effectiveness of dimethyl hydrogen phosphite for solvent extraction are shown in the table below. The feedstock is a lube distillate obtained from Mid-Continent petroleum crude. A single batch extraction was employed in all examples in accordance with the above operating procedure. The rafiinate and extract from Example A were sent to settlers for sludge removal prior to testing. The rafiinate con tained 1.6 weight percent sludge and the extract stream 12.3 Weight percent.

aliphatic hydrocarbon raffinate phase from a relatively aromatic hydrocarbon extract phase.

Example Feedstock A B C D Operating Conditions:

Solvent Dosage Dimethyl Hydrogen Phosphite, Vol. percen 200 200 300 400 Toluene, Vol. percent 200 200 100 Temperature, F 180 150 180 180 Mixing Time, Minute 30 30 30 30 Settling Time, Minutes 15 15 15 15 Stripping Gas for Paffimte Nitrogen Steam Nitrogen Nitrogen Stripping Gas for Extract Steam Steam Nitrogen Nitrogen Yields, Wt. percent:

Ralfinate 32. 0 60.3 82. 1 84. 8 Extr 0S. 0 39.7 17.9 15. 2 Tests on Rafiinate:

Gravity, API 28.1 28.3 29.4 29. 2 Viscosity, SUSll00 215 212 Waxy 198 Pour, F 90 60 50 100 100 Refractive Index, 7m 1. 5001 1. 4900 1. 4910 1. 4898 1. 4908 Tests on Extract:

Gravity, API Viscosity, SUS/l00 F Pour, F Refractive Index, 129

to obtain two liquid phases and separating a relatively 35 2. The process of claim 1 wherein the dimethyl hydrogen phosphite to hydrocarbon ratio is about 0.5 :1 to 10:1 and the extraction temperature is about 75 to 300 F.

3. The process of claim 1 in which the mixture contains an olefinic hydrocarbon which reacts with the dimethyl hydrogen phosphite to form a sludge.

4. The process of claim 3 in which the dimethyl hydrogen phosphite to hydrocarbon ratio is about 0.5:1 to 10:1 and the extraction temperature is about 75 to 300 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,567,228 Morrell et a1 Sept. 11, 1951 

1. A PROCESS FOR THE EXTRACTION OF AN AROMATIC HYDROCARBON FROM A LIQUID HLYDROCARBON MIXTURE CONTAINING THE SAME AND AN ALIPHATIC HYDROCARBON WHICH COMPRISES CONTACTING SAID MIXTURE WITH DIMETHYL HYDROGEN PHOSPHITE TO OBTAIN TWO LIQUID PHASES AND SEPARATING A RELATIVELY ALIPHATIC HYDROCARBON RAFFINATE PHASE FROM A RELATIVELY AROMATIC HYDROCARBON EXTRACT PHASE. 